Hello, I'm Joao Patricio, I'm an Electronic Engineer.
I work since 3 years ago with Internet of Things and other microcontroller projects. I work with circuit's design and firmware develloping
Usually i Work with pic, ATmel, Arduino (Uno, Mega, Nano and Due), ESP8266 (boards like ESP12 and NodeMcu)
For my firmwares I use C/C++ and Lua Script
About Your project:
1 - the wiring.
The HC-05 serial communication pins operate at 3V3. so to connect to the Nano, you need a voltage divider.
NanoRx ---- HCTx
NanoTx --- (voltage divider) --- HCRx.
Otherwise, HC-05 may be damaged.
2 - Assuming that point 1 is ok.
To respond to AT commands, pin 34 must be high (pullup resistor to 3V3). This pin is relatively hidden on the side of the plate. Put it on high level and restart the module.
3 - When in command mode, the baudRate of HC-05 changes to 38400. No matter what you initially set in the code, this is the default of it when restarted in command mode
I hope it answers your problem.